Sunday, January 27, 2008

IIT JEE Revision - Acid Catalysed Hydration of Alkynes

In the presence of acid (H2SO4) and HgSO-4, a molecule of water adds to the triple bond at 348K.

The catalyst in this reaction is HgSO4 (Mercuric sulphate).

The final products of this reaction are carbonyl compounds aldehydes and ketones.

Initially enol is formed which is raidly converted into an equilibrium mixture containing keto form in excess.

Enol is so called because it contains 'ene' (double bond) and an alcoholic group (ol).

Addition of water to Ethyne or acytelene: Acetylene is passed into water (at about 330K) containing 60% H2SO4 and about 1% mercuric sulphate (HgSO4) as a catalyst, acetaldehyde is formed.

In the first step 'ethenol' is formed and in the second step the rearrangement of it takes place and its isomer 'acetaldehyde' is formed.

The conversion of enol form into keto form is termed tautomerism

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